U.S. patent application number 10/507587 was filed with the patent office on 2005-05-19 for shock absorbing pad for a vehicle.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Fukuyama, Taku, Murakami, Takeshi, Okada, Takaharu.
Application Number | 20050104414 10/507587 |
Document ID | / |
Family ID | 29239895 |
Filed Date | 2005-05-19 |
United States Patent
Application |
20050104414 |
Kind Code |
A1 |
Murakami, Takeshi ; et
al. |
May 19, 2005 |
Shock absorbing pad for a vehicle
Abstract
The present invention the related to a shock absorption pad for
a vehicle for protecting occupant's lower legs. The shock
absorption pad according to the present invention on which an
occupant's foot is placed is attached on a surface of a toe board.
The shock absorption pad includes a first shock absorption layer
provided on the occupant's foot-placing side for absorbing an
impact generated in a boundary region at which an energy absorption
load of a vehicle body becomes different in a deformation process
of the vehicle body at a vehicle crash, and a second shock
absorption part provided on the toe board's side for absorbing an
impact generated in a region in which the energy absorption load is
high.
Inventors: |
Murakami, Takeshi;
(Toyota-shi, Aichi, JP) ; Fukuyama, Taku;
(Ikoma-shi, Nara, JP) ; Okada, Takaharu;
(Nagoya-shi, Aichi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
1, Toyota-cho, Toyota-shi
Aichi
JP
471-8571
SEKISUI KASEIHIN KOGYO KABUSHIKI KAISHA
4-4, Nishitemma 2-chome, Kita-ku, Osaka-shi
Osaka
JP
530-8565
CHUGAI CO., LTD
Chugal Bldg., 21-11, Chiyoda 5-chome, Naka-ku
Nagoya-shi, Aichi
JP
460-0012
|
Family ID: |
29239895 |
Appl. No.: |
10/507587 |
Filed: |
September 13, 2004 |
PCT Filed: |
March 28, 2003 |
PCT NO: |
PCT/JP03/04037 |
Current U.S.
Class: |
296/187.05 |
Current CPC
Class: |
B60R 2021/0414 20130101;
B60R 21/04 20130101; B60R 2021/0046 20130101; B60N 3/066
20130101 |
Class at
Publication: |
296/187.05 |
International
Class: |
B62D 025/20 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 29, 2002 |
JP |
2002-97231 |
Claims
1. A shock absorption pad for a vehicle which is attached on a
surface of a toe board and on which an occupant's foot is placed,
comprising: a first shock absorption part provided on the
occupant's foot-placing side for absorbing an impact force
generated in a boundary region at which an energy absorption load
of a vehicle body becomes different in a deformation process of the
vehicle body at a vehicle crash; and a second shock absorption part
provided on the toe board's side for absorbing an impact generated
in a region in which the energy absorption load is high.
2. The shock absorption pad for a vehicle as claimed in claim 1,
wherein the first shock absorption part is divided in a plane over
the occupant's foot-placing area so as to lower an in-plane
rigidity of the first shock absorption part during its compressive
deformation, and an energy absorption load per unit area of the
first shock absorption part is set lower than that of the second
shock absorption part.
3. The shock absorption pad for a vehicle as claimed in claim 1,
wherein the first shock absorption part is comprised of a plurality
of projections formed all over the occupant's foot-placing area on
an upper surface of the second shock absorption part.
4. The shock absorption pad for a vehicle as claimed in claim 1,
wherein the first and second shock absorption parts are formed from
a foam-molded element and are formed by one of multi-layering
foam-molded elements, laminating foam-molded elements with an
adhesive, and integral foam-molding.
5. The shock absorption pad for a vehicle as claimed in claim 1,
wherein the shock absorption pad is a foam-molded component made
from a styrene modified polyethylene resin.
6. A shock absorption pad for a vehicle which is attached on a
surface of a toe board and on which an occupant's foot is placed,
wherein the shock absorption pad is a foam-molded component made
from a resin and is provided with a plurality of projections on the
occupant's foot-placing side, said projections being spaced from
each other.
7. The shock absorption pad for a vehicle as claimed in claim 2,
wherein the first and second shock absorption parts are formed from
a foam-molded element and are formed by one of multi-layering
foam-molded elements, laminating foam-molded elements with an
adhesive, and integral foam-molding.
8. The shock absorption pad for a vehicle as claimed in claim 3,
wherein the first and second shock absorption parts are formed from
a foam-molded element and are formed by one of multi-layering
foam-molded elements, laminating foam-molded elements with an
adhesive, and integral foam-molding.
9. The shock absorption pad for a vehicle as claimed in claim 2,
wherein the shock absorption pad is a foam-molded component made
from a styrene modified polyethylene resin.
10. The shock absorption pad for a vehicle as claimed in claim 3,
wherein the shock absorption pad is a foam-molded component made
from a styrene modified polyethylene resin.
Description
TECHNICAL FIELD
[0001] The invention relates to a shock absorption pad for use in a
vehicle for protecting occupant's lower legs at the time of a
vehicle crash, and more specifically relates to a shock absorption
pad for use in a vehicle having a stepwise shock absorption
characteristic.
BACKGROUND ART
[0002] Concerning the structure for protecting occupant's lower
legs, JP, 2000-103367, A and JP, 2000-326870, A disclose
inventions, wherein the structure of a vehicle itself is configured
to have the desired shock absorption characteristic. Further, JP,
5-330341, A and JP, 6-17097, B, disclose inventions, wherein the
foam material that absorbs energy is arranged in foot resting
portions in the cabin so as to protect the occupant's lower
legs.
[0003] However, giving a desired shock absorbent function to the
structure of the vehicle itself involves design changes of vehicle
body structure and may require additional material and parts to
achieve the desired shock absorbent function. So it is predicted to
increase the cost.
[0004] Moreover, in the case of using a shock absorption material,
such as a foam material, since the shock absorption characteristic
is fixed, the impact load whose magnitude varies in the deformation
process of the vehicle body at the time of a vehicle crash cannot
be absorbed effectively.
[0005] The energy absorption load of the vehicle in the deformation
process at the time of a vehicle crash is highly set up in a rear
portion of a front side member rather than in a front portion of
the front side member, or is highly set up in an inclined portion
that extends from the rear end of the front side member backward
and downward along the surface of a toe board of a lower dash
panel.
[0006] Therefore, the deceleration that acts on the vehicle body
becomes suddenly high for a short time interval in the boundary
region where the energy absorption load in the rear portion or the
inclined portion changes in the direction that becomes high. Then,
the rear portion or the inclined portion will deform under the
set-up energy absorption load to absorb energy.
[0007] In this case, the vehicle after the crash can be stopped by
virtue of the high energy absorption load due to the deformation of
the rear portion or the inclined portion. At this time, the impact
on occupant's lower legs can be reduced by shock absorption
material, such as a foam material. However, it is difficult to
achieve adequate compatibility between this reduction and the
reduction of the impact force which becomes suddenly high for a
short time interval in the boundary region at which the energy
absorption load of the vehicle body changes.
[0008] For the solution to this problem, it is conceivable that by
changing the structure of the vehicle body, the energy absorption
load difference is made small so as to attain the smooth energy
absorption load characteristic. However, this will result in
increased manufacturing cost of the body structure.
DISCLOSURE OF INVENTION
[0009] It is a general object of the present invention to provide a
shock absorption pad for use in a vehicle that can reduce more
effectively the various shocks applied to occupant's lower legs
without significantly changing the body structure.
[0010] A more specific object of the present invention is to
provide the shock absorption pad for a vehicle, which is equipped
with the shock absorption characteristic configured to be variable
in a multi-stepped manner according to the various shocks that act
on occupant's lower legs, whereby the shock applied to occupant's
lower legs can be reduced more effectively.
[0011] In order to achieve the above-mentioned objects, there is
provided according to the present invention a shock absorption pad
for a vehicle which is attached on a surface of a toe board and on
which an occupant's foot is placed, comprising: a first shock
absorption part provided on the occupant's foot-placing side for
absorbing an impact force generated in a boundary region at which
an energy absorption load of a vehicle body becomes different in a
deformation process of a vehicle body at a vehicle crash; and a
second shock absorption part provided on the toe board's side for
absorbing an impact generated in a region in which the energy
absorption load is high.
[0012] According to this arrangement, since the shock absorption
pad is provided with two shock absorption parts whose shock
absorption characteristics are different from each other, different
types of impact loads applied on occupant's lower legs, which are
generated in the course of a vehicle body's deformation process,
can be effectively reduced by these two shock absorption parts,
respectively. That is, the impact, which becomes suddenly high for
a short time in the boundary region in which the energy absorption
load of vehicle becomes different, can be absorbed by the
deformation of the first shock absorption part, whereby the shock
over occupant's lower legs which is likely to become momentarily
high can be reduced. Then, the impact generated second in the
region in which the energy absorption load of the vehicle body
becomes high can be absorbed by the deformation of the second shock
absorption part, whereby the shock over occupant's lower legs can
be reduced. Especially, since the first shock absorption part is
provided on the side on which occupant's legs may be laid, the
shock absorption characteristic can easily be tuned so that it
adapts to the impact that reaches its peak suddenly for a short
time in the boundary region in which the energy absorption load of
vehicle becomes different.
[0013] It is noted that the above-mentioned shock absorption pad
has the characteristic such that an amount of deformation per unit
load in a direction perpendicular to the surface of the toe board
is lower in the second shock absorption part than in the first
shock absorption part.
[0014] Further, according to the shock absorption pad, wherein the
first shock absorption part is divided in a plane over the
occupant's foot-placing area so as to lower an in-plane rigidity of
the first shock absorption part during its compressive deformation,
and an energy absorption load per unit area of the first shock
absorption part is set lower than that of the second shock
absorption part, it becomes possible to form the shock absorption
parts whose shock absorption characteristics are different from
each other. That is, as the result of lowering an in-plane rigidity
of the first shock absorption part, the first shock absorption part
becomes easy to deform in a good follow-up manner enough to absorb
the impact that reaches its peak suddenly for a short time in the
boundary region of the energy absorption load of vehicle body,
whereby the respective shocks over occupant's lower legs can be
advantageously absorbed, respectively.
[0015] Further, according to the shock absorption pad, wherein the
first shock absorption part is comprised of a plurality of
projections formed all over the occupant's foot-placing area on an
upper surface of the second shock absorption part, it becomes
possible to advantageously absorb the respective shocks over
occupant's lower legs, respectively. Furthermore the tuning of the
compression load characteristic of each projection for implementing
the aforementioned desired shock absorption characteristic becomes
easy.
[0016] Further, according to the shock absorption pad, wherein the
first and second shock absorption parts are formed from a
foam-molded element and are formed by one of multi-layering
foam-molded elements, laminating foam-molded elements with an
adhesive, and an integral foam-molding, it becomes possible to
advantageously absorb the respective shocks over occupant's lower
legs, respectively, with a simple arrangement. In the case of
adopting an integral foam-molding process among others, since it is
possible to integrally foam-molding the shock absorption pad in a
metallic mold, the shock absorption pad with the aforementioned
desired shock absorption characteristic can be produced in volume
at low cost.
[0017] Additionally, in the case of the shock absorption pad being
a foam-molded component made from a styrene modified polyethylene
resin, advantageous effects resulting from the characteristic
peculiar to styrene modified polyethylene resin, such as
outstanding dimensional stability and form retention
characteristic, good shock absorption characteristic, and the
characteristic of being difficult to generate wear powder and
undesired noise against rubbing, can be gained.
[0018] Other objects, features and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1A is a cross-sectional view for diagrammatically
illustrating the assembled state of the shock absorption pad 10
according to the present invention.
[0020] FIG. 1B is a perspective view for illustrating the assembled
state of the shock absorption pad 10 in more detail.
[0021] FIG. 2A is a plan view of the shock absorption pad 10
according to the present invention.
[0022] FIG. 2B is a cross-sectional view taken on the line S-S of
FIG. 2A.
[0023] FIG. 3 is a diagram for showing a test result as to a shock
absorption characteristic of the shock absorption pad 10 according
to the present invention.
[0024] FIG. 4 is a diagram for showing the load data on a time
series picked up at the lower leg portion of a dummy through a real
vehicle crash examination.
[0025] FIG. 5A is a diagram for illustrating the state of the
deformed vehicle body at the first impact.
[0026] FIG. 5B is a diagram for illustrating the state of the
deformed vehicle body at the second impact.
[0027] FIG. 6A is a plan view for showing the shock absorption pad
90 as a contrast for the shock absorption pad 10 according to the
present invention.
[0028] FIG. 6B is a cross-sectional view of the shock absorption
pad 90 taken on the line S-S of FIG. 6A.
BEST MODE FOR CARRYING OUT THE INVENTION
[0029] Hereafter, the preferred embodiments according to the
present invention are explained with reference to the drawings.
[0030] FIG. 1A is a cross-sectional view for diagrammatically
illustrating the shock absorption pad 10 according to the present
invention, which is assembled in a vehicle body in place, seen from
the vehicle side. FIG. 1B is a perspective view for illustrating
the installed shock absorption pad 10 in more detail.
[0031] The shock absorption pad 10 is disposed on a toe board 12
that extends forward and upward in a slanting direction from the
front end of the floor panel 11 (arrow X shown in FIG. 1A indicates
the front direction). The toe board 12 defines an inclined area
(hereafter, this inclined area is referred as "foot-placing area")
on which occupant's legs 70 are to be placed, as shown in FIG. 1A.
Generally, the shock absorption pad 10 is placed in the
above-mentioned foot-placing area of the toe board 12 and attached
to the toe board 12 with clips, etc. Generally, the shock
absorption pad 10 is covered with a floor carpet 13 on which
occupant's legs 70 are to be placed directly.
[0032] FIG. 2 is a diagram showing the shock absorption pad 10
according to the present invention, wherein FIG. 2A is a plan view
of the shock absorption pad 10, and FIG. 2B is a view taken on line
S-S of FIG. 2A. It is noted that the shock absorption pad 10 shown
in FIG. 2A has an outside shape different from that of the shock
absorption pad 10 shown in FIG. 1B.
[0033] As shown in FIG. 2B, the shock absorption pad 10 according
to the present invention has a first shock absorption layer 20 on
the side on which occupant's legs 70 are put, and has a second
shock absorption layer 30 on the toe board 12 side. These shock
absorption layers 20 and 30 may be integrally formed from synthetic
resin foam, such as polystyrene-based resin, polyethylene-based
resin, polypropylene-based resin, polyester-based resin, and
styrene modified polyethylene resin, or flexible material, such as
urethane and rubber.
[0034] However, the shock absorption pad 10 is preferably formed
from styrene modified polyethylene resin. Styrene modified
polyethylene resin is obtained by impregnated polymerization of the
styrene system monomer with a polyethylene system resin particle.
Styrene modified polyethylene resin contains a styrene ingredient
in the range from 40 to 90 wt %, more preferably, contains a
styrene ingredient in the range from 50 to 85 wt %, most preferably
contains a styrene ingredient in the range from 55 to 75 wt %.
[0035] Here, the foam-molded component made of styrene modified
polyethylene resin has an advantage over the foam-molded component
made of polyethylene based resin or polypropylene based resin in
terms of dimensional stability and form maintenance characteristic
because of the general characteristics of styrene modified
polyethylene resin. Moreover, when compared under the same
condition of an expansion ratio, the foam-molded component made of
styrene modified polyethylene resin can absorb a large amount of
shock. Furthermore, unlike the foam-molded component of polystyrene
based resin, the foam-molded component of styrene modified
polyethylene resin resists becoming brittle and thus cannot break
easily. Furthermore, the foam-molded component of styrene modified
polyethylene resin generates neither an undesired noise nor wear
powder due to rubbing.
[0036] Therefore, the styrene modified polyethylene resin which has
the above advantageous characteristics is considered as a suitable
material for the shock absorption pad 10, since the shock
absorption pad is required to demonstrate the effective shock
absorption characteristic in a limited thickness and a limited size
and is disposed at the floor portion in the cabin on which
occupant's legs are put.
[0037] The first shock absorption layer 20 of the shock absorption
pad 10 includes a plurality of projections 24 formed on the second
shock absorption layer 30. These projections 24 are formed within
the area corresponding to the above-mentioned foot-placing area,
and are preferably formed substantially all over the area
corresponding to the foot-placing area. As shown in FIG. 2A, these
projections 24 may be arranged in a lattice pattern so as to form
channels in the shape of a cross when seen from above. In addition,
these projections 24 may be arranged at regular interval spacing
where each projection 24 is spaced from its adjacent projection 24
at a constant distance. Further, these projections 24 may be
arranged in a staggered configuration by making each of projections
24 staggered in a longitudinal or lateral direction.
[0038] Moreover, each of these projections 24 may have various
outside shapes, such as a square, a rectangle, a circle, an
ellipse, etc. Moreover, each projection 24 does not need to have a
constant cross-section along the projection direction. Furthermore,
the tip of each projection 24 may be configured so that it may be
pressed by occupant's soles at a surface or a point.
[0039] Moreover, the size and arrangement of each projection 24 may
be determined so that an occupant's sole can be supported by
several projections 24. The total area of the projections 24 to be
pressed by an occupant's sole may correspond to 30-60% of a
footprint of an average occupant, and the area of each projection
24 may be in the range from about 200 mm.sup.2 to about 600
mm.sup.2. Moreover, projections 24 may have a height difference
locally and the height of some projections 24 may be different from
that of other projections 24.
[0040] However, the shock absorption characteristic of the shock
absorption pad 10 is dependent on various factors, such as a
material property of the shock absorption pad 10, and the thickness
of each shock absorption layers 20 and 30. So it should be
understood that the shock absorption pad with outside shape,
arrangement, and size, etc., not specified above is within the
limits of this invention insofar as it has the shock absorption
characteristic as mentioned below.
[0041] FIG. 3 is a diagram for explaining the shock absorption
characteristic of the shock absorption pad 10 according to the
present invention, in which a load-distortion curve of the shock
absorption pad 10 according to the present invention is shown. The
load-distortion curves of other shock absorption pads are also
shown for contrast. Specifically, the load-distortion curve of the
first comparative pad is indicated by a broken line, which first
comparative pad is formed from the same material as the shock
absorption pad 10 according to the present invention but doesn't
have the projections 24. The load-distortion curve of the second
comparative pad is indicated by a chain double-dashed line, which
second comparative pad is formed from a material softer than the
material used for the shock absorption pad 10 according to the
present invention and doesn't have the projections 24. It is noted
that these load-distortion curves are based on the measurements
made on a test piece of each shock absorption pad using appropriate
measuring and testing equipment. It is also noted that these
load-distortion curves indicate the distortion characteristic of
each shock absorption pad against the compression load along the
direction perpendicular to the toe board 12 (see the direction Z in
FIG. 1A).
[0042] As shown in FIG. 3, the load-distortion curve (solid line)
of the shock absorption pad 10 according to the present invention
changes significantly at the predetermined distortion level
.epsilon..sub.p. This means that the load-distortion characteristic
of the shock absorption pad 10 according to the present invention
varies in a multi-stepped manner (in this embodiment, a two-stepped
manner) at the predetermined distortion level .epsilon..sub.p. That
is, the shock absorption pad 10 according to the present invention
exhibits a shock absorption characteristic which is equivalent to
that of the second comparative pad when deformation of the first
shock absorption layer 20 begins, and exhibits a shock absorption
characteristic equivalent to the first comparative pad when
deformation of the first shock absorption layer 20 is completed and
deformation of the second shock absorption layer 30 begins. In
other words, with virtue of a plurality of projections 24, the
first shock absorption layer 20 can have the shock absorption
characteristic equivalent to the second comparative pad that is
formed from comparatively soft material, even though the first
shock absorption layer 20 is formed from the same material as the
first comparative pad.
[0043] The inventors of the present invention carried out the crash
examination using a real vehicle equipped with the shock absorption
pad 10 in order to verify the effect of the shock absorption pad 10
equipped with the step-wise shock absorption characteristic, and
obtained the following results.
[0044] FIG. 4 shows the load data on the time series picked up at
the lower leg portion of a dummy through the real vehicle crash
examination. In FIG. 4, time t=0 is the time of the moment the
vehicle's front end came into contact with the barrier. In FIG. 4,
the measurement data (dotted line) of the first comparative pad and
the measurement data (chain double-dashed line) of the second
comparative pad are also shown as contrast. Hereafter, the
examination result shown in FIG. 4 will be discussed with reference
to the FIG. 5 that diagrammatically shows the vehicle's deformation
process at the time of vehicle crash, and FIG. 3.
[0045] When the vehicle crash begins at time t=0, at first the
engine room part 40 (see FIG. 1A) begins to deform. Then, when the
deformation of the engine room part 40 advances gradually, the load
on the lower legs of the dummy begins to increase. Then, the load
on the dummy's lower legs reaches the first peak value at the time
t=t1 when the deformation of the engine room part 40 has
substantially reached its full potential. Hereafter, this crash
stage is referred as "first impact".
[0046] As shown in FIG. 4, the load at the first impact is a
momentary shock that is generated over a relatively shorter time
interval as compared with the load at the second impact that will
be described later. That is, the time interval from start-up time
to fall time of the first impact is shorter than that of the second
impact. Thus, the energy to be absorbed at the first impact is less
than that at the second impact.
[0047] Referring to FIG. 4, at the first impact, the load exerted
on the dummy's lower legs is higher in the case of using the first
comparative pad than in the case of using the shock absorption pad
10 according to the present invention or the second comparative
pad. Referring to FIG. 3, this result can be derived from the fact
that at the first impact the load F.sub.a1 corresponding to the
distortion .epsilon..sub.a1 of the first comparative pad is larger
than the load F.sub.b1 corresponding to the distortion
.epsilon..sub.b1 Of the shock absorption pad 10 according to the
present invention or the second comparative pad. On the other hand,
there is substantially no difference in the load exerted on the
dummy's lower legs between the case of using the shock absorption
pad 10 according to the present invention and the case of using the
second comparative pad. This result can be derived from the fact
that there is substantially no difference in distortion level
between these shock absorption pads at the first impact.
[0048] It can be understood from this test result that the
deformation of the first comparative pad cannot follow the
instantaneous load at the first impact and causes a large load to
be transmitted to the dummy's lower legs. To the contrary, the
shock absorption pad 10 according to the present invention can
deform instantaneously in response to the instantaneous load at the
first impact and thus can effectively reduce the load to be
transmitted to the dummy's lower legs.
[0049] Subsequently, after the deformation of the engine room part
40 is completed, the toe board 12 begins to be pushed up and
backward, as shown in FIG. 5B. That is, the toe board 12 begins to
deform and move such that the sole of a dummy is pushed up. At this
time, as the amount of movement of the whole vehicle decreases by
the end of deformation of the engine room part 40, the dummy moves
forward with respect to the vehicle due to its inertial force. That
is, the dummy moves forward with its sole abutted against the toe
board 12. Because of these two effects, the load of the dummy's
lower legs increases gradually and reaches the second peak value at
the time t=t2. Hereafter, this crash stage is referred as "second
impact".
[0050] The time interval from the beginning of this second impact
to its end is longer than the time interval related to the
aforementioned first impact. Thus, the energy to be absorbed at the
second impact is much greater than that at the first impact.
[0051] Referring to FIG. 4, at the second impact, the load exerted
on the dummy's lower legs is greater in the case of using the
second comparative pad than in the case of using the shock
absorption pad 10 according to the present invention or the first
comparative pad. Referring to FIG. 3, this result can be derived
from the fact that because the second comparative pad absorbs the
smallest amount of energy when compared under the same condition of
an amount of deformation, it had already deformed beyond its full
potential (i.e. its distortion level had reached approximately
.epsilon..sub.max indicated in FIG. 3) before absorbing all the
energy that should be absorbed by the time t=t2. That is, the
second comparative pad had entered a state where it cannot deform
any more by the time t=t2, and thus the sole of a dummy had
substantially entered a state where it was in contact with the
rigid body by the time t=t2.
[0052] On the other hand, at the second impact, there is
substantially no difference in the load exerted on the dummy's
lower legs between the case of using the shock absorption pad 10
according to the present invention and the case of using the first
comparative pad. Referring to FIG. 3, this result can be derived
from the fact that the load F.sub.a2 corresponding to the
distortion .epsilon..sub.a2 of the first comparative pad at the
second impact is substantially equal to the load F.sub.b2
corresponding to the distortion .epsilon..sub.b2 of the shock
absorption pad 10 according to the present invention at the second
impact.
[0053] From the above test result, it can be said that the shock
absorption pad 10 according to the present invention can achieve
the lowest values of load exerted on the dummy's lower legs both at
the first impact and at the second impact and protect occupant's
lower legs most effectively. This is because at the first impact in
which the instantaneous load is generated, the occupant's lower
legs are protected by the first shock absorption layer 20, which
can easily deform and absorb a small amount of energy per unit area
(which unit area includes the area of the first shock absorption
layer 20 not provided with projections 24), while at the second
impact in which a relatively long-duration load is generated due to
the upward movement of the panel in the foot-placing area, the
occupant's lower legs are protected by the second shock absorption
layer 30, which absorbs a relatively large amount of energy per
unit area. Thus, according to the shock absorption pad 10 according
to the present invention, since it has the shock absorption
characteristic that varies in stages according to the first impact
and second impact which occur in stages in the course of the
vehicle crash process, it becomes possible to protect occupant's
lower legs effectively.
[0054] It is noted that the thickness of the first shock absorption
layer 20, the number and arrangement of projections, etc., are
determined so that the energy at the first impact can be absorbed
only by the deformation of the first shock absorption layer 20,
while the thickness and area, etc., of the second shock absorption
layer 30 are determined so that the second shock absorption layer
30 cannot deform beyond its maximum level at the second impact
(i.e. so that the amount of deformation of the second shock
absorption layer 30 cannot reach the elastic limit). However, it is
also noted that the overall thickness of the shock absorption pad
10 will be subjected to the constraint from the viewpoint of
sufficient cabin space.
[0055] The shock absorption pad 10 used for the above-mentioned
test had a thickness of about 30 mm, the thickness of the first
shock absorption layer 20 was about 10 mm, and the total area of
the top surfaces of the projections 24 was about 55% of the total
area of the shock absorption pad 10. This shock absorption pad 10
showed the desired shock absorption characteristic. That is, during
the first impact the shock absorption pad 10 exhibited the shock
absorption characteristic equivalent to the first comparative pad,
and at the time at which the second impact began (i.e. the time
t=t3 in FIG. 4) it deformed at the distortion revel
.epsilon..sub.p, which corresponds to the transition point of the
shock absorption characteristic, and during the second impact it
exhibited the shock absorption characteristic equivalent to the
second comparative pad without deforming beyond its maximum level.
However, these design matters depend on the amount of energies to
be absorbed at the first and second impact and thus depend on the
structure of the vehicle body. The shock absorption characteristic
of the shock absorption pad 10 may be adjusted based on a real
crash test, analysis, etc., for every type of vehicle to implement
the aforementioned desired shock absorption characteristic.
[0056] Here, since the shock absorption pad 10 according to the
present invention has a plurality of projections 24 formed in a
discrete pattern (i.e. spaced arrangement) as mentioned above, and
further has the first shock absorption layer 20 on the side of
occupant's legs 70, the adjustment of the shock absorption
characteristic for realizing the aforementioned desired
characteristic becomes easy and problems arising from normal use
can be avoided.
[0057] On the contrary, with reference to FIG. 6A and FIG. 6B, the
shock absorption pad 90 equipped with the protruding lines 93
formed in a crisscross pattern is shown. The first shock absorption
layer 91 of this shock absorption pad 90 has higher in-plane
rigidity as compared with the first shock absorption layer 20 of
the present invention equipped with projections 24 not connected
with each other in a plane over the foot-placing area, and thus the
adjustment of the shock absorption characteristic of the shock
absorption pad 90 for realizing the aforementioned desired
characteristic becomes complicated. That is, the deformation of the
portion of the protruding lines 93 that actually abuts against the
sole involves the deformation of the other portion that actually
doesn't abut against the sole. So the adjustment of the shock
absorption characteristic should be done considering such a
deformation characteristic. Furthermore, with such high in-plane
rigidity, the first shock absorption layer 91 cannot deform in a
good follow-up manner against an instantaneous load such as the
above-mentioned first impact load.
[0058] Similarly, in the case of the shock absorption pad 95 (not
shown) equipped with the first shock absorption layer 20 on the
side of the toe board 12 instead of on the side of the occupant's
leg 70, the adjustment of the shock absorption characteristic of
the shock absorption pad 90 for realizing the aforementioned
desired characteristic becomes complicated because all the
projections 24 abut against the surface of the toe board 12. That
is, the pressure on the shock absorption pad 95 from the sole
causes the deformation of substantially all the projections 24 and
furthermore there may be a difference in the amount of the
deformation between each projection 24. So the adjustment of the
shock absorption characteristic of the shock absorption pad 90 for
realizing the aforementioned desired characteristic becomes very
difficult. Moreover, in the case of realizing the aforementioned
desired characteristic, since the compression load per unit
projection becomes small, the projections 24 may easily become flat
when the occupant's legs 70 press strongly them or when the
occupant's legs 70 are placed only on them. In this case, the shock
absorption pad 95 will not fully achieve its function in the actual
crash because of the flattened projections 24. Moreover, such a
shock absorption pad 95 isn't likely to keep its shock absorption
characteristic for a long time and thus does not have good
durability.
[0059] In contrast to this, the shock absorption pad 10 according
to the present invention, which is equipped with projections 24 not
connected with each other, has the structure in which only some
projections 24 which are actually supporting the sole can deform.
So the desired shock absorption characteristic is realizable with
easy adjustment, setting up a suitable compression load per unit
projection so as not to cause the projections 24 to deform easily
during normal use.
[0060] Further, the present invention is not limited to the
above-described embodiments, and variations and modifications may
be made without departing from the scope of the present
invention.
[0061] For example, in the above-mentioned embodiments, although
the shock absorption pad 10 according to the present invention is
molded in one piece to have the first shock absorption layer 20 and
the second shock absorption layer 30, the shock absorption pad 10
may be constituted by forming each shock absorption layer from a
different material and by laminating together these shock
absorption layers.
[0062] In addition, the shock absorption pad 10 according to the
present invention may be constituted by forming each shock
absorption layer from the same material with different density and
by laminating together these shock absorption layers, or may be
constituted by laminating together foam-molded absorption layers
made from the same kind of or a different kind of synthetic resin.
Furthermore, the shock absorption pad 10 according to the present
invention may be an integrally-molded component made by expanding
the same kind of or a different kind of synthetic resin foaming
beads with a different expansion ratio in a metal mold. Although
reference is made to the two-stage shock absorption characteristic
in the above-mentioned embodiment, it is also possible to realize a
three or more stage shock absorption characteristic by forming
additional shock absorption layers.
* * * * *